Some types of identification systems employ a heatshrinkable element that becomes snugly applied to an article after being subjected to heat. An example of this is a heatshrinkable marker sleeve used to identify an electrical wire or similar object. The marker sleeve has a diameter larger than that of the wire and fits loosely about the wire when first inserted on it. The sleeve is thereafter subjected to hot air so as to shrink and tightly conform to the periphery of the wire.
Heatshrinkable marker sleeves are made of various types of plastic films or resins that are unidirectionally oriented so as to shrink upon the application of heat. It is generally necessary to apply identification data to the marker sleeve, which may consist of a serial number, name, or other alphanumeric data, in order to identify a specific article to which the sleeve is applied. A user may apply identification data by printing systems typically available in various plants or offices, such as by a typewriter or computer printer, or manually with a writing pen.
Plastic materials of which identification devices such as marker sleeves are made cannot always be printed conveniently or acceptably with the above types of printing systems. A printable coating, therefore, is applied to the devices that is capable of receiving and retaining printed indicia. Various types of printable coatings may be employed with non-heatshrinkable identification devices that will exhibit good adhesion to the devices and good retention of the applied printed data. However, these same coatings are not suitable for heatshrinkable identification devices because they lose adhesion and become wrinkled when subjected to heat.
One solution to this problem is the use of hot stamping techniques to apply alphanumeric indicia onto heatshrinkable sleeves. This is not altogether satisfactory because hot stamping is a labor intensive operation and requires special equipment which many companies do not normally employ. A second prior art solution involves the use of radiation treated inks and requires special equipment for printing the sleeves, or modification of equipment such as typewriters. This technique also is not satisfactory because of the expense of the special equipment and materials required, and because the printed images exhibit relatively poor adhesion to the sleeve and generally can be rubbed off with finger pressure.
No suitable printable coatings for heatshrinkable identification devices have been available, so far as we are aware, prior to the invention disclosed herein. The deficiencies of the prior art printable coatings and inadequacies of the alternative known procedures discussed above were the impetus for the development of the present invention.